The present invention relates to a rotary control valve with a variable area orifice that communicates with a bypass channel. This arrangement effectively eliminates cavitation and noise in the valve in any intermediate position. More specifically, the invention relates to a rotary control valve with a variable area orifice in the control element that communicates with a bypass channel in any intermediate or modulated position. Variable area rotary control valves are widely used in the petroleum refining and chemical industries. Several types of these valves with rotary control elements have been disclosed including the following U.S. Pat. Nos. 3,443,793, 3,558,100, 3,612,102, and 4,212,321.
The present invention may be described as an improvement over the known valves that control flow velocity and pressure drop of fluids through various connected flow conduits. The current technology uses rotary valves, which, when rotated through predetermined angular rotation, provide a controlled variation of the How path from the fully open position to the shut position. The full open position provides maximum flow with variable flow decreasing to the completely shut position.
In addition to controlling the flow characteristics (i.e., velocity and pressure), the rotary valves currently used often contain a noise reduction means to suppress the noise inherently created by the restriction of the high velocity flow of fluids through a rotary control valve. These noise suppression means are primarily diverters of the fluid flow through a labyrinth of multiple pathways forming a tortuous path that creates a restricted flow coupled with a dissipation of energy, resulting in substantially reduced noise levels.
The '321 patent provides means to vary a flow path using two opposed divergent spiral grooves, one of which is in register with the upstream port and the other of which is in register with the downstream port. When the spiral grooves are rotated in the flow path, flow is diverted into a tortuous path thereby creating a controlled restriction of flow and resultant noise suppression. When the valve in the '321 patent is open, the valve provides an unrestricted flow path. The '321 patent also describes a valve in which noise is further reduced by placing other noise silencing means within the flow valve element of the valve as well as within the two opposed divergent spiral grooves.
The noise suppression of the '321 patent presents several difficulties. Primarily, the noise suppression means are subject to wear, erosion, and clogging. Valves employing these flow control and noise suppression means require substantial, periodic maintenance. Maintenance often times requires replacement of the control member or the noise silencing means. At a minimum, because the design of the rotary valves described in the prior art precludes the design of a top entry valve body, maintenance to such a valve requires that the valve be completely removed from the line, disassembled, retrimmed and then reinstalled at considerable expense with interruption of the line.